upper collecting system of the urinary tract, i.e., kidney and ureter. It is done in cases where excretory or retrograde pyelography has failed or contraindicated, or when a nephrostomy tube is in place or delineation of upper tract is desired. It is commonly used to diagnose upper tract obstruction, hydronephrosis, and ureteropelvic junction obstruction. In this, radiocontrast dye is injected into the renal pelvis and X-rays are taken. It provides detailed anatomy of the upper collecting system. As it is an invasive procedure, it is chosen when other non-invasive tests are non confirmatory or contraindicated and patient monitoring is required prior and after the procedure. Retrograde pyelogram A retrograde pyelogram is a medical imaging procedure in which a radiocontrast agent is injected into the ureter in order to visualize the ureter, bladder, and kidneys with fluoroscopy or radiography, using plain X-rays. The flow of contrast (up from the bladder to the kidney) is opposite the usual outbound flow of urine, hence the retrograde ("moving backwards") name. A retrograde pyelogram may be performed to find the cause of blood in the urine, or to locate the position of a stone or narrowing, tumour or clot, as an adjunct during the placement of ureteral stents. It can also be used ureteroscopy, or to delineate renal anatomy in preparation for surgery. Retrograde pyelography is generally done when an intravenous excretory study (intravenous pyelogram or contrast CT scan) cannot be done because of renal disease or allergy to intravenous contrast. Relative contraindications include the presence of infected urine, pregnancy (because of radiation), or allergy to the contrast. Because a pyelogram involves cystoscopy, it may cause sepsis, infection or bleeding, and may also cause nausea and vomiting. The dye may also be toxic to the kidneys. Before the procedure, a person is usually asked to complete a safety check assessing for potential risks, such as pregnancy or allergy. They may be asked to take an enema, and not to eat for some hours. An intravenous drip is inserted and a person is given some sedation before a cystoscope, which is a flexible tube, is inserted into the bladder via the urethra. 10 ml of contrast is usually injected during cystoscopy, which is where a flexible tube is inserted into the bladder and to the lower part of the ureter. Fluoroscopy, or dynamic X-rays, is typically used for visualization. The procedure is usually done under general